A Denver judge mistakenly concluded police officers executed a search warrant that lacked probable cause, the Colorado Supreme Court decided Monday, rejecting arguments that a detective failed to properly check a confidential informant’s car for narcotics prior to a controlled drug purchase.

The justices determined that the circumstances of the police investigation into Scott McKay, taken altogether, gave a magistrate sufficient grounds to sign off on a search warrant. Even if the investigation was not ironclad, “a fair probability existed that a search of McKay’s car and home would reveal contraband or evidence of a crime,” concluded Justice William W. Hood III for the Court.

The Fourth Amendment requires probable cause for a search warrant, which means there must be sufficient facts to indicate evidence of criminal activity at the place intended for searching. An affidavit presented to a magistrate does not need to describe every part of the investigation, but must include details that would alert the magistrate that probable cause may not exist for a warrant.

In McKay’s case, the affidavit police provided for a search warrant described how a confidential informant disclosed that McKay had recently sold the informant methamphetamine. McKay was reportedly distributing the substance from his home and other places, and had prior drug arrests.

Police used the informant to make two purchases of meth from McKay. Before each transaction, a detective searched the informant to make sure he had neither drugs nor money on him. Police gave him money and surveilled the drug purchase. Afterward, the detective searched the informant again to ensure he had no drugs other than those McKay reportedly gave him.

The police sought a search warrant, using it to seize drugs and firearms from McKay’s home and car. Prosecutors charged him with drug possession and with three counts of possession of a weapon by a prior offender.

McKay challenged the legality of the warrant, arguing that the confidential informant drove to the two drug buys and could have had meth in his car. Although the police affidavit never mentioned the informant had driven to meet McKay – or that the detective had neglected to search his car – District Court Judge Eric M. Johnson sided with McKay.

In Johnson’s reading of the affidavit, “although it says that the CI was searched, in neither instance does it indicate that the car was searched. So the drugs could have been in the car,” he observed. Johnson noted that the affidavit described police as having “followed” the informant to McKay’s house. To the judge, that indicated the parties were driving, and the magistrate should not have issued a warrant without an indication that police ensured there were no drugs in the informant’s car.

Johnson also cast doubt on the information’s representation that he previously bought meth from McKay, saying “there’s no information to support that.”

The Denver District Attorney’s Office appealed directly to the Supreme Court. “The district court’s interpretation is suspect. At best, the affidavit is ambiguous regarding the informant’s use of any car,” wrote Deputy District Attorney Richard F. Lee, adding that Johnson should have deferred to the magistrate’s judgment.

McKay’s lawyer argued the judge arrived at the correct conclusion. It was the confidential informant’s first time with Denver police, and he had no track record of reliability. Officers had evidently not observed McKay sell to anyone else at the residence in suburban north Denver, and it would have been “crucial” for the magistrate to know that the detective failed to search the car of a known drug buyer prior to making a controlled purchase.

But the Supreme Court decided that Johnson should have deferred to the magistrate’s evaluation of the police affidavit and was wrong to suppress evidence from the drug buys.

“The issuing magistrate could have drawn the commonsense inference that this experienced narcotics investigator engaged in reasonable due diligence by properly searching the CI to confirm that he did not have access to any other drugs or money during the buys,” Hood wrote in the Court’s opinion.

The decision, however, still allows McKay to request a hearing in the trial court to challenge the truthfulness of statements made in the affidavit.

The case is People v. McKay.